Chapter 9
Catalytic Hydroprocessing of
Liquid Biomass for Biofuels Production
Stella Bezergianni
Additional information is available at the end of the chapter
http://dx.doi.org/10.5772/52649
1. Introduction
The depletion of world petroleum reserves and the increased concern on climate change has
stimulated the recent interest in biofuels. The most common biofuels are based on energy
crops and their products, i.e. vegetable oil for Fatty Acid Methyl Esters (FAME) biodiesel [1]
and sugars/starch for bioethanol. However these first generation biofuels and associated
production technologies face several considerations related to their economic and social im‐
plications regarding energy crops cultivation, by-products disposal, necessity for large in‐
vestments to ensure competitiveness and the “food versus fuel” debate.
As a result, second generation biofuel technologies have been developed to overcome the
limitations of first generation biofuels production [2]. The goal of second generation biofuel
processes is to extend biofuel production capacity by incorporating residual biomass while
increasing sustainability. This residual biomass consists of the non-food parts of food crops
(such as stems, leaves and husks) as well as other non-food crops (such as switch grass, ja‐
tropha, miscanthus and cereals that bear little grain). Furthermore the residual biomass po‐
tential is further augmented by industrial and municipal organic waste such as skins and
pulp from fruit pressing, waste cooking oil etc. One such technology is catalytic hydropro‐
cessing, which is an alternative conversion technology of liquid biomass to biofuels that is
lately raising a lot of interest in both the academic and industrial world and is the proposed
subject of this chapter.
Catalytic hydroprocessingis a key process in petrochemical industry for over a century ena‐
bling heteroatom (sulfur, nitrogen, oxygen, metals) removal, saturation of olefins and aro‐
matics, as well as isomerization and cracking [3]. Due to the numerous applications of
catalytic hydroprocessing, there are several catalytic hydroprocessing units in a typical re‐
finery including distillate hydrotreaters and hydrocrackers (see Figure 1). As a result several
© 2013 Bezergianni; licensee InTech. This is an open access article distributed under the terms of the Creative
Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,
distribution, and reproduction in any medium, provided the original work is properly cited.
refinery streams are treated with hydrogen in order to improve final product quality includ‐
ing straight-run naphtha, diesel, gas-oils etc. The catalytic hydroprocessing technology is
evolving through the new catalytic materials that are being developed. Even though hydro‐
processing catalysts development is well established [4], the growing demand of petroleum
products and their specifications, which are continuously becoming stricter, have created
new horizons in the catalyst development in order to convert heavier and lower quality
feedstocks [5]. Furthermore the expansion of the technology to bio-based feedstocks has also
broadened the R&D spam of catalytic hydrotreatment.
Thermal
process
Heavy
fractions
upgrading
Catalytic
pyrolysis
Catalytic
reforming
Heavy Gasoil
Hydrotreating
Lubricants
process
Naphtha
Light Vacuum Gasoil
Heavy Vacuum Gasoil
Coke
Asphalt
Lubricants
Thermal processing
Hydrocracking mid-distillate
Hydrocracking gasoline
Light hydrocarbons C1-C4
Isomerization product
Reformate
Gasoline polymerization
Alkylate
Alkylation gasoiline
Straight-run kerozene
Straight-run diesel
Catalytic pyrolysis gasoline
Catalytic pyrolysis
F
in
al
p
ro
ce
ss
in
g
a
n
d
b
le
n
d
in
g
Fuel gas
Liquid gas
Aviation
Diesel
Unleaded
Heating
Gasoline
oil
Fuels
Hydrotreating
Hydrotreating
Fuel gas and gasoline
diesel
Hydrocracking
Atm.
Distillation
Vacuum
Distillation
Isomerization
Polymerization
Alkylation
Thermal
process
Heavy
fractions
upgrading
Catalytic
pyrolysis
Catalytic
reforming
Heavy Gasoil
Hydrotreating
Lubricants
process
Naphtha
Light Vacuum Gasoil
Heavy Vacuum Gasoil
Coke
Asphalt
Lubricants
Thermal processing
Hydrocracking mid-distillate
Hydrocracking gasoline
Light hydrocarbons C1-C4
Isomerization product
Reformate
Gasoline polymerization
Alkylate
Alkylation gasoiline
Straight-run kerozene
Straight-run diesel
Catalytic pyrolysis gasoline
Catalytic pyrolysis
F
in
al
p
ro
ce
ss
in
g
a
n
d
b
le
n
d
in
g
Fuel gas
Liquid gas
Aviation
Diesel
Unleaded
Heating
Gasoline
oil
Fuels
Hydrotreating
Hydrotreating
Fuel gas and gasoline
diesel
Hydrocracking
Atm.
Distillation
Vacuum
Distillation
IsomerizationIsomerization
PolymerizationPolymerization
AlkylationAlkylation
Figure 1. Catalytic hydroprocessing units within a refinery, including distillate hydrotreating and hydrocracking
Catalytic hydroprocessing of liquid biomass is a technology that offers great flexibility to the
continuously increasing demands of the biofuels market, as it can convert a wide variety of
liquid biomass including raw vegetable oils, waste cooking oils, animal fats as well as al‐
gal oils into biofuels with high conversion yields. In general this catalytic process technolo‐
gy allows the conversion of triglycerides and lipids into paraffins and iso-paraffins within
the naphtha, kerosene and diesel ranges. The products of this technology have improved
characteristics as compared to both their fossil counterparts and the conventional biofuels
including high heating value and cetane number, increased oxidation stability, negligible
acidity and increased saturation level. Besides the application of this catalytic technology for
the production of high quality paraffinic fuels, catalytic hydroprocessing is also an effective
Liquid, Gaseous and Solid Biofuels - Conversion Techniques300
technology for upgrading intermediate products of solid biomass conversion technologies
such as pyrolysis oils and Fischer-Tropsch wax (Figure 2). The growing interest and invest‐
ments of the petrochemical, automotive and aviation industries to the biomass catalytic hy‐
droprocessing technology shows that this technology will play an important role in the
biofuels field in the immediate future.
Gasification
Wax
Solid Biomass
Pyrolysis oilPyrolysis Catalytic
Hydroprocessing
Liquid Biomass
Gasoline
Diesel
Fischer-Tropsch
SynthesisGasification
Wax
Solid Biomass
Pyrolysis oilPyrolysis Catalytic
Hydroprocessing
Liquid Biomass
Gasoline
Diesel
Fischer-Tropsch
Synthesis
Figure 2. Catalytic hydroprocessing for biomass conversion and upgrading towards fuels production
In the sections that follow, the basic technical characteristics of catalytic hydrotreatment are
presented including a description of the process, reactions, operating parameters and feed‐
stock characteristics. Furthermore key applications of catalytic hydroprocessing of liquid bi‐
omass are outlined based on different feedstocks including raw vegetable oils, waste
cooking oils, pyrolysis oils, Fischer-Tropsch wax and algal oil, and some successful demon‐
stration activities are also presented.
2. Technical characteristics of catalytichydrotreatment
The catalytic hydrotreatment of liquid biomass converts the contained triglycerides/lipids
into hydrocarbons at high temperatures and pressures over catalytic material under excess
hydrogen atmosphere. The catalytic hydrotreatment of liquid biomass process is quite simi‐
lar to the typical process applied to petroleum streams, as shown in Figure 3. A typical cata‐
lytic hydrotreatment unit consists of four basic sections: a) feed preparation, b) reaction, c)
product separation and d) fractionation.
In the feed preparation section the liquid biomass feedstock is mixed with the high pressure
hydrogen (mainly from gas recycle with some additional fresh make-up hydrogen) and is
preheated before it enters the reactor section. The reactor section consists normally of two
hydrotreating reactors, a first guard mild hydrotreating reactor and a second one where the
main hydrotreating reactions take place. Each reactor contains two or more catalytic beds in
order to maintain constant temperature profile throughout the reactor length. Within the re‐
actor section all associated reactions take place, which will be presented in more detail at a
later paragraph.
Catalytic Hydroprocessing of Liquid Biomass for Biofuels Production
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The reactor product then enters the separator section where, after it is cooled down, it enters
the high pressure separator (HPS) flash drum in which the largest portion of the gas and liq‐
uid product molecules are separated. The gas product of the HPS includes
